Materials having gas barrier properties and flexibility are required for: food packages in the form of a film, a sheet, a bag, a bottle, and the like; packings for a container to seal a beverage bottle with a bottle cap, seal a medical bottle with a lid, and the like; medical infusion solution bags; tire tubes; and the like.
For example, since a material for a food package requires flexibility and high gas barrier properties, laminates having a gas barrier layer containing an ethylene-vinyl alcohol-based copolymer or polyamide and a flexible resin layer are widely used. Since a material for a packing for a container requires flexibility and gas barrier properties, NR (natural rubber) and IIR (butyl rubber) are generally used. Since a material for a medical infusion solution bag requires flexibility and gas barrier properties, vinyl chloride is generally used. Since a material for a tire tube requires flexibility and high gas barrier properties, IIR is generally used.
IIR, however, needs complex vulcanization after molding to exhibit flexibility in a shaped article using IIR while IIR is excellent in flexibility [durometer hardness (type A) of approximately 65] and gas barrier properties [OTR of approximately 4000 cc·20 μm/(m2·day·atm)]. Although being excellent in gas barrier properties, such an ethylene-vinyl alcohol-based copolymer and polyimide are insufficient in flexibility and thus a laminate of a barrier layer of such a resin and a flexible resin layer is used as a food package, and as a result, limitation and complexity are brought to molding process. Having not so high gas barrier properties, NR is disadvantageous in longer shelf life of the contents when used as a material for a packing for containers and the like. Shaped articles using vinyl chloride are concerned about harmful influence on the environment due to generation of hydrogen chloride gas during incineration disposal.
As polymer materials excellent in flexibility and not requiring vulcanization, thermoplastic elastomers, such as SEBS (styrene-ethylene butylene-styrene triblock copolymer) and SEPS (styrene-ethylene propylene-styrene triblock copolymer), are proposed. However, depending on the use, the gas barrier properties are sometimes insufficient.
In comparison, as a resin composition applicable to a food package, a packing for a container, a medical infusion solution bag, a tire tube, and the like, a resin composition is proposed containing a block copolymer having a polymer block comprising vinyl aromatic monomer units and a polymer block comprising isobutylene units and an ethylene-vinyl alcohol-based copolymer (refer to Patent Document 1). This polymer composition is described as excellent in flexibility and gas barrier properties. However, when the polymer composition described in Patent Document 1 is produced over a long period of time, the production becomes difficult due to cross-linking of the polymers, causing difficulty in stable production of the polymer composition.